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Home My WebLink AboutWPO202000044 Stormwater Management Maintenance Agree. 2021-03-18SHIMP ENGINEERING, P.C. Design Focused Engineering February 171h, 2021 County VSMP Review Albemarle County Regarding: Tenpas Residence SWM Calculation Packet Dear Reviewer: Enclosed is the Stormwater Management Calculations Packet for the Tenpas Residence project. The enclosed calculations demonstrate compliance with the runoff requirements set forth in 9VAC25-870-55. This project will disturb an area of 4.21 acres. Stormwater Quantity complies with 9VAC25-870-66.D through sheetflow conditions from all impervious areas. All areas of disturbance will be graded so as to create sheet flow conditions. Where runoff concentrates at the new culvert (#2) beneath the driveway, a 40-ft level spreader will be installed to convert the concentrated flow to sheet flow. Stormwater Quality complies with 9VAC25-870-65 through the dedication of 3.28 acres of Open Space within B & D soils. If you have any questions please feel free to contact me via e-mail at justin@shimp-engineering.com or by telephone at 434-227-5140. Sincerely, Justin Shimp Shimp Engineering, P.0 Contents: Post-Dev Runoff Quantity Calculations: Post-Dev Culvert Drainage Map Post-Dev Runoff Quality Calculations: VRRM New-Dev Spreadsheet Summary Independent Reports: Excerpt from NRCS Soil Report NOAA Precipitation Report Post-Dev Runoff Quality Calculations: VRRM New-Dev Spreadsheet Summary Virginia Runoff Reduction Method Worksheet DEQ Virginia Runoff Reduction Method New Development Compliance Spreadsheet - Version 3.0 LIMP Design Specifications List: 2013 Draft Stds & Specs Site Summary Project Title: Tenpas Residence, VSMP ( WP0202000044) Date: 10/28/2020, by Alb. Co. Total Rainfall= 43 inches Site Land Cover Summary A soils BSoils CSails DSolls Totals %of Total Forest/Open (acres) 0.00 0.57 0.00 2.71 3.28 44 Managed Turf(acres) 1 0.00 3.74 0.00 0.00 3.74 50 Impervious Cover(acres) 1 0.00 0.40 0.00 0.07 0.47 6 7.49 100 Site Tv and Land Cover Nutrient Loads Site Rv 0.18 Treatment Volume fts 4,885 TP Load (lb/yr) 3.07 TN Load (Ib/yr) 21.96 Total TP Load Reduction Required (Ib/yr) 0.00 " TP LOAD REDUCTION NOT REQUIRED Site Compliance Summary Total Runoff Volume Reduction (ft) 0 Total TP Load Reduction Achieved (lb/yr) 0.00 Total TN Load Reduction Achieved (Ib/yr) 0.00 Remaining Post Development TP Load 3.07 (lb/yr) Remaining TP Load Reduction (lb/yr) 0.00 Required -'No further TP load reduction required Summary Print Virginia Runoff Reduction Method Worksheet Drainage Area Summary DA. A D.A. B D.A. C D.A. D D.A. E Total Forest/Open (acres) 0.00 0.00 0.00 0.00 0.00 0.00 Managed Turf (acres) 0.00 0.00 0.00 0.00 0.00 0.00 Impervious Cover(acres) 0.00 0.00 0.00 0.00 0.00 0.00 Total Area (acres) 0.00 0.00 0.00 0.00 0.00 0.00 Drainage Area Compliance Summary D.A. A D.A. B D.A. C D.A. D D.A. E Total TP Load Reduced (lb/yr) 1 0.00 0.00 1 0.00 1 0.00 0.00 0.00 TN Load Reduced (lb/yr) 1 0.00 0.00 1 0.00 1 0.00 0.00 0.00 Summary Print Virginia Runoff Reduction Method Worksheet ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Runoff Volume and CN Calculations 1-year storm 2-year storm 10-year storm Target Rainfall Event (in) 1 0.00 0.00 0.00 Drainage Areas RV&CN Drainage Area Drainage Area Drainage Area Drainage Area Drainage Area CN 0 0 0 0 0 RR (it) 0 0 0 0 0 1-year return period RV wo RR (ws-In) 0.00 0.00 0.00 0.00 0.00 RV w RR (wsin) 0.00 0.00 0.00 0.00 0.00 CN adjmted 0 0 0 0 0 2-year return period RV wa RR (.:in) 0.00 0.00 0.00 0.00 0.00 RV w RR (wsin) 0.00 0.00 0.00 0.00 0.00 CN adjusted 0 0 0 0 0 10-year return period RVwo RR (wsin) 0.00 0.00 0.00 0.00 0.00 RV w RR Iwsin) 0.00 0.00 0.00 0.00 0.00 cN adjusted 0 0 0 0 0 Summary Print Post-Dev Runoff Quantity Calculations: Post-Dev Culvert Drainage Map 100 0 100 200 300 / 9vFF10 Scale: 1 "=100' SHIMPENGINEERING, PC ----- - ENGINEERING-LODMWNG -PROJECT MANr1GEMENT , — — 595 _ 012 E NION ST PNONKt <Q4) 229-0110 ; FUTURE P0on- /r'\ Ap CNARLO=SMI , VA 22902 JVSTNOSNIMP-ENOINEERINO.COM \ \ / ♦ , 3 / \ SOILS (TYP \ M � 7 I I p� r � / S19 _ �S01LS'I(TYP) i ��P� 9 "4��AY EL HSG B EPT�C��G 6p 001041 " DRAINFIELD ti I / TENPAS RESIDENCE POSTDEV CULVERT DRAINAGE AREA MAP NEW 2 —1 LF �5y CMP CULVERT 0.95% (CULVIT EW 40—FT LNCINE€R EVEL SPREADER I I � I I CULVERT #2 �I;: -- •,' "»�,' «« :�», � ego DA 1.46 AC EW HOUSE' -7 µ ^ ;f. ; » •' FFE=.615.20' BFET605.20' OPEN SPACE o .ram»�,y!*•'' :'»'+'•TO BE DEDICATED; 3.28 AC /' �� /�� »"� / �\,»,`,�»*�,F,'»yF»'»y,�'.•*�•,;»F•+',,+»'�,`»y:Fi»'»F•F:»F»F•"*»F»' • ;: �»�»»»»»»'»:^;;'/ �\»,»''»V,»:;i�S�;D:'.,:,•,',',»•,`»•,.V.»: ,pop RESE& ' DRAINFI�LD NEW 35-LF 18" CMP CULVERT Deg ----- 0 124 % (CULVERT #1) CULVERT #1 HSG1.90 AC`• p EX DITCH # V. GRAVEL i X. GATE ENTRANCE N f �o \ EX. FF�NLE -fL -�f - PuADPI ROAD EX. CU /-NE�1 GARME, FFE�0t?10.20' 1 1109 .0• Y� t \- HISG B6004 ti / EX. PONDX. �\q . CU WESLEY HSG B sf ac in ft It It TENPAS RESDENCE min in in in in cfs cfs cfs cfs CIS Le%el Spreader ft It ft CULVERT DA DA PIPE DIA. MATERIAL INV IN INV OUT LENGTH SLOPE Manningsn C CA Tc I-1n I-1yr I - Tyr I-10yr Q-iin Q-1yr Q-Tyr Q-10yr Pipe Capacity Length(Calc) Length (Design) Depth 1 2 82874 63405 1.90 1.46 18 15 CMP CMP 598 595.5 597.5 595.3 35 21 1.43% 0.022 0 95% 0 022 0.35 0.67 0.35 0.51 5 5 1 1 3.03 3.03 3.67 3.67 5.52 5.52 0.67 0.51 2A2 1 54 2A4 1.07 3.68 2.81 7.42 3.72 - - - 37 40 06 ` Length = 13ft per 1-cfs from 1 an storm Independent Reports: Excerpt from NRCS Soil Report NOAA Precipitation Report USDA United States Department of Agriculture MRCS Natural Resources Conservation Service A product of the National Cooperative Soil Survey, a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local participants Custom Soil Resource Report for Albemarle County, Virginia August 19, 2020 3 N W WWN � I I Custom Soil Resource Report Soil Map Il��l • g •� gigis scale. •, 9'S0"ry MMO 710WO 710" 710BOD MMO ]11[ 1111m 3 3 MaP SeL: IA,710 ff piinted m A poftk (8.5' x 1179,E N Met s 0 W 10D MD 300 AD Z00 40800 ,Zr Map prolecbm: Web Wouatw Cwwdnas:WGS&1 EdgetmUIMZ17N WGS84 9 Custom Soil Resource Report Albemarle County, Virginia 513—Belvoir loam, 2 to 7 percent slopes Map Unit Setting National map unit symbol: 2xxxg Elevation: 360 to 1,540 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: Not prime farmland Map Unit Composition Belvoir and similar soils: 80 percent Minor components: 5 percent Estimates are based on observations, Description of Belvoir descriptions, and transects of the mapunit. Setting Landform: Swales Landform position (two-dimensional): Summit Landform position (three-dimensional): Base slope Down -slope shape: Concave Across -slope shape: Concave Parent material: Residuum weathered from granite and gneiss Typical profile A - 0 to 12 inches: loam Bt1 - 12 to 19 inches: loam Btx - 19 to 28 inches: sandy loam B't2 - 28 to 45 inches: clay loam 2C - 45 to 79 inches: clay loam Properties and qualities Slope: 2 to 7 percent Depth to restrictive feature: 16 to 30 inches to fragipan Drainage class: Somewhat poorly drained Runoff class: Very high Capacity of the most limiting layer to transmit water (Ksat) moderately high (0.06 to 0.20 in/hr) Depth to water table: About 12 to 24 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Very low (about 2.8 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 3w Hydrologic Soil Group: D Hydric soil rating: No Minor Components Delila Percent of map unit: 5 percent Moderately low to 13 Custom Soil Resource Report Landform: Drainageways Landform position (two-dimensional): Footslope Landform position (three-dimensional): Head slope, tread Down -slope shape: Concave Across -slope shape: Convex Hydric soil rating: Yes 713-13raddock loam, 2 to 7 percent slopes Map Unit Setting National map unit symbol: kbfb Elevation: 360 to 1,230 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: All areas are prime farmland Map Unit Composition Braddock and similar soils: 80 percent Estimates are based on observations, descriptions, and transacts of the mapunit. Description of Braddock Setting Landform: Fans Landform position (three-dimensional): Tread Down -slope shape: Convex Across -slope shape: Linear Parent material: Alluvium and colluvium derived from acid crystalline rocks Typical profile H1 - 0 to 8 inches: loam H2 - 8 to 79 inches: clay Properties and qualities Slope: 2 to 7 percent Depth to restrictive feature: More than 80 inches Drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 1.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: High (about 9.1 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 2e Hydrologic Soil Group: B Hydric soil rating: No 14 Custom Soil Resource Report 7C—Braddock loam, 7 to 15 percent slopes Map Unit Setting National map unit symbol: kbfc Elevation: 430 to 1,490 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: Farmland of statewide importance Map Unit Composition Braddock and similar soils: 80 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Braddock Setting Landform: Fans Landform position (three-dimensional): Tread Down -slope shape: Convex Across -slope shape: Linear Parent material: Alluvium and colluvium derived from acid crystalline rocks Typical profile H1 - 0 to 8 inches: loam H2 - 8 to 79 inches: clay Properties and qualities Slope: 7 to 15 percent Depth to restrictive feature: More than 80 inches Drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 1.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: High (about 9.1 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 3e Hydrologic Soil Group: B Hydric soil rating: No 15 Custom Soil Resource Report 14C—Chester loam, 7 to 15 percent slopes Map Unit Setting National map unit symbol: kb81 Elevation: 380 to 1,690 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: Farmland of statewide importance Map Unit Composition Chester and similar soils: 80 percent Estimates are based on observations, Description of Chester descriptions, and transects of the mapunit. Setting Landform: Hillslopes Landform position (two-dimensional): Summit Landform position (three-dimensional): Interfluve Down -slope shape: Convex Across -slope shape: Convex Parent material: Residuum weathered from granite and gneiss Typical profile H1 - 0 to 7 inches: loam H2 - 7 to 41 inches: clay loam H3 - 41 to 79 inches: loam Properties and qualities Slope: 7 to 15 percent Depth to restrictive feature: More than 80 inches Drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat) (0.57 to 1.98 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Moderate (about 6.9 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 3e Hydrologic Soil Group: B Hydric soil rating: No Moderately high to high Custom Soil Resource Report 81 B—Thurmont loam, 2 to 7 percent slopes Map Unit Setting National map unit symbol: kbfh Elevation: 440 to 1,160 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: All areas are prime farmland Map Unit Composition Thurmont and similar soils: 80 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Thurmont Setting Landform: Interfluves Landform position (two-dimensional): Summit Landform position (three-dimensional): Interfluve Down -slope shape: Convex Across -slope shape: Convex Parent material: Colluvium derived from granite, granodiorite, Typical profile H1 - 0 to 10 inches: loam H2 - 10 to 46 inches: clay loam H3 - 46 to 56 inches: loam H4 - 56 to 79 inches: cobbly sandy loam Properties and qualities Slope: 2 to 7 percent Depth to restrictive feature: More than 80 inches Drainage class: Well drained Runoff class: Medium and granite gneiss Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 1.98 in/hr) Depth to water table: About 48 to 79 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Moderate (about 8.3 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 2e Hydrologic Soil Group: B Hydric soil rating: No IVA Custom Soil Resource Report 81C—Thurmont loam, 7 to 15 percent slopes Map Unit Setting National map unit symbol: kbfj Elevation: 490 to 1,480 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: Farmland of statewide importance Map Unit Composition Thurmont and similar soils: 80 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Thurmont Setting Landform: Interfluves Landform position (two-dimensional): Backslope Landform position (three-dimensional): Interfluve Down -slope shape: Convex Across -slope shape: Convex Parent material: Colluvium derived from granite, granodiorite, Typical profile H1 - 0 to 10 inches: loam H2 - 10 to 46 inches: clay loam H3 - 46 to 56 inches: loam H4 - 56 to 79 inches: cobbly sandy loam Properties and qualities Slope: 7 to 15 percent Depth to restrictive feature: More than 80 inches Drainage class: Well drained Runoff class: Medium and granite gneiss Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.57 to 1.98 in/hr) Depth to water table: About 48 to 79 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Moderate (about 8.3 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 3e Hydrologic Soil Group: B Hydric soil rating: No WV Custom Soil Resource Report 96B—Delila loam, 2 to 7 percent slopes Map Unit Setting National map unit symbol: 2v7kc Elevation: 360 to 1,540 feet Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: Not prime farmland Map Unit Composition Delila and similar soils: 75 percent Estimates are based on observations, Description of Delila descriptions, and transects of the mapunit. Setting Landform: Drainageways Landform position (two-dimensional): Footslope Landform position (three-dimensional): Head slope, tread Down -slope shape: Concave Across -slope shape: Convex Parent material: Colluvium derived from igneous rock Typical profile A - 0 to 9 inches: loam Btg - 9 to 54 inches: clay Cg - 54 to 79 inches: sandy clay loam Properties and qualities Slope: 2 to 7 percent Depth to restrictive feature: More than 80 inches Drainage class: Poorly drained Runoff class: Very high Capacity of the most limiting layer to transmit water (Ksat) low (0.00 to 0.06 in/hr) Depth to water table: About 0 to 12 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Moderate (about 8.2 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4w Hydrologic Soil Group: D Hydric soil rating: Yes Very low to moderately 19 Custom Soil Resource Report W—Water Map Unit Setting National map unit symbol: kbgk Mean annual precipitation: 25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost -free period: 195 to 231 days Farmland classification: Not prime farmland Map Unit Composition Water: 100 percent Estimates are based on observations, descriptions, and transects of the mapunit. 20 NOAA Atlas 14, Volume 2, Version 3 Location name: Free Union, Virginia, USA* t Latitude: 38.1687°, Longitude:-78.5928° Elevation: 611.19 H** � " source: ESRI Maps "source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M. Bonnin, D. Martin, B. Lin, T. Pa2ybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland PF tabular I PF graphical I Maps & aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1 Average recurrence interval (years) Duration 7 �� 2 5 10 25 50 100 200 500 1000 0.338 0.406 0.479 0.540 0.617 0.666 0.719 0.770 0.834 0.886 5-min (0306-0.374) (0.367-0.449) (0.432-0.529) (0.486-0.596) (0.547-0.673) (0.593-0.733) (0.636-0.793) (0.676-0.850) (0.722-0.924) (0.760-0.986) 0.540 0.648 0.766 0.862 0.972 1.06 1.14 1.22 1.32 1.39 10-min F� (0.489-0.597) (0.586-0.717) (0.692-0.846) (0.777-0.952) (0.871-1.07) (0.943-1.17) 1 (1.01-1.26) 1 (1.07-1.35) 1 (1.14-1.46) 1 (1.19-1.55) 0.674 0.814 0.968 1.09 1.23 1.34 1.44 1.54 1.66 1.75 15-min (0.611-0.746) (0.736-0.901) (0.875-1.07) (0.982-1.20) (1.10-1.36) (1.19-1.48) (1.27-1.59) 1 (1.35-1.70) 1 (1.44-1.84) 1 (1.50-1.95) 0.923 1.12 1.37 1.58 1.82 2.01 2.20 2.39 2.63 2.82 30-min (0.836-1.02) 1 (1.01-1.24) 1 (1.24-1.52) 1 (1.42-1.74) 1 (1.63-2.01) 1 (1.79-2.22) 1 (1.95-2.43) 1 (2.10-2.64) 1 (2.28-2.92) 1 (2.42-3.14) 1.15 1.47 1.76 2.05 2.42 2.3 3.04 3.35 3.77 4.12 0-min 6 (1.04-1.27) 1 (1.27-1.56) 1 (1.59-1.94) 1 (1.85-2.27) 1 (2.17-2.67) 1 (2.43-3.01) 1 (2.69-3.35) 1 (2.94-3.70) 1 (3.27-4.18) 1 (3.53-4.59) 1.38 1.68 2.11 2.48 2.96 3.37 3.79 4.23 4.85 5.38 F2-hr (1.23-1.55) 1 (1.50-1.88) 1 (1.88-2.36) 1 (2.21-2.78) 1 (2.62-3.31) 1 (2.96-3.76) 1 (3.31-4.23) 1 (3.66-4.73) 1 (4.15-5.45) 1 (4.55-6.06) 1.51 1.84 2.30 2.70 3.23 3.68 4-.1 51 F-4-.6-4-T-55-4-T-5-.9-4-1 3-hr (1.35-1.71) 1 (1.63-2.07) 1 (2.04-2.60) 1 (2.39-3.05) 1 (2.84-3.64) 1 (3.22-4.14) 1 (3.60-4.67) 1 (3.99-5.23) 1 (4.53-6.04) 1 (4.98-6.73) 1.94 2.35 2.92 3.44 4.13 4.75 5.39 6.10 7.12 8.02 6-hr (1.74-2.18) 1 (2.10-2.65) 1 (2.60-3.29) 1 (3.04-3.86) 1 (3.64-4.65) 1 (4.14-5.32) 1 (4.65-6.06) 1 (5.20-6.86) 1 (5.97-8.03) 1 (6.62-9.08) 2.45 2.96 3.68 4.35 5.30 6.13 7.05 8.07 9.59 11.0 12-hr (2.18-2.78) 1 (2.63-3.36) 1 (3.27-4.18) 1 (3.85-4.94) 1 (4.63-5.99) 1 (5.31-6.94) 1 (6.03-T99) 1 (6.80-9.15) 1 (7.91-10.9) 1 (8.88-12.5) 3.03 3.67 4.67 5.52 6.76 7.83 9.00 70.3 12.2 13.9 24-hr (2.73-3.38) 1 (3.31-4.09) 1 (4.20-5.22) 1 (4.94-6.15) 1 (6.02-7.52) 1 (6.91-8.68) 1 (7.88-9.97) 1 (8.91-11.4) 1 (10.4-13.6) 1 (11.6-15.4) 3.57 4.32 5.48 6.43 7.81 8.97 10.2 11.6 13.6 15.3 2-day (3.22-3.97) (3.90-4.81) (4.94-6.10) (5.79-7.15) (6.97-8.66) (7.95-9.94) (8.98-11.3) (10.1-12.9) (11.7-15.1) (13.0-17.0) 3.80 4.60 5.83 6.84 8.31 9.53 10.9 12.3 14.4 76.2 3-day (3.45-4.21) 1 (4.18-5.09) 1 (5.29-6.46) 1 (6.19-7.57) 1 (7.47-9.17) 1 (8.51-10.5) 1 (9.62-12.0) 1 (10.8-13.6) 1 (12.5-15.9) 1 (13.9-17.9) 4.03 4.88 6.19 7.25 8.80 10.1 11.5 13.0 15.2 17.0 4-day (3.68-4.45) 1 (4.45-5.38) 1 (5.64-6.82) 1 (6.60-7.98) 1 (7.97-9.68) 1 (9.08-11.1) 1 (10.3-12.6) 1 (11.5-14.3) 1 (13.3-16.7) 1 (14.8-18.9) 4.68 5.84 7.05 8.19 9.84 11.2 12.7 14.2 16.5 18.3 7-day P� (4.28-5.13) 1 (5.16-6.17) 1 (6.44-7.72) 1 (7.47-8.97) 1 (8.92-10.8) 1 (10.1-12.3) 1 (11.3-13.9) 1 (12.6-15.6) 1 (14.4-18.1) 1 (15.9-20.2) 5.32 6.38 7.87 9.07 10.7 12.1 13.5 15.1 17.2 19.0 10day F� (4.89-5.78) 1 (5.88-6.93) 1 (7.23-8.55) 1 (8.32-9.84) 1 (9.81-11.7) 1 (11.0-13.1) 1 (12.2-14.7) 1 (13.5-16.4) 1 (15.3-18.8) 1 (16.7-20.8) 6.99 8.33 10.1 11.4 13.2 14.7 16.1 17.6 19.7 21.2 20i18y P� (6.53-7.52) 1 (7.78-8.95) 1 (9.38-10.8) 1 (10.6-12.2) 1 (12.3-14.2) 1 (13.5-15.7) 1 (14.9-17.3) 1 (16.1-19.0) 1 (17.9-21.2) 1 (19.2-23.0) 8.57 10.2 12.0 13.4 15.2 16.6 18.0 19.3 21.1 22.4 30-day (8.06-9.15) 1 (9.55-10.8) 1 (11.3-12.8) 1 (12.6-14.3) 1 (14.2-16.2) 1 (15.5-17.7) 1 (16.7-19.2) 1 (17.9-20.7) 1 (19.4-22.6) 1 (20.6-24.1) 10.7 12.B 14.8 16.3 18.4 19.9 21.3 22.7 24.5 25.8 45ilay (10.1-11.4) 1 (11.9-13.4) 1 (13.9-15.7) 1 (15.4-17.3) 1 (17.2-19.5) 1 (18.6-21.1) 1 (19.9-22.6) 1 (21.1-24.2) 1 (22.7-26.2) (23.8-27.6) 12.5 14.8 17.0 18.7 20.8 22.4 23.8 25.2 27.0 28.3 60-day (11.9-13.3) (14.0-15.6) (16.1-18.0) (17.7-19.7) (19.6-22.0) (2L0-23.6) (22.4-25.2) (23.7-26.7) (25.2-28.7) (26.4-30.1) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top